Accelerometer

ABSTRACT

An antiskid braking system which includes valve means for controlling the application of operating pressure to the brakes, so as to rapidly release and then more gradually allow application of the brakes when a skid is indicated, the valve means being operated by the output of a fluid amplifier means which, in turn, is operated by signals from a linear accelerometer that moves in the path of the vehicle and an angular accelerometer that rotates with the wheel, each accelerometer including a seismic mass positioned by impinging fluid discharged from an adjacent outlet and relatively movable to vary the restriction of the fluid discharged to produce signals indicating acceleration and deceleration.

[ 1 Dec. 16, 1975 ACCELEROMETER Vernon R. Fish, 525 Meadowbrook Ave.,Orange, Calif. 92665 [22] Filed: Apr. 15, 1974 [21] Appl. No.: 460,993

Related US. Application Data [6:] Division of Ser. No. 277,676, Aug. 3,1972, Pat. No.

[76] Inventor:

[52] US. Cl 73/510; 73/515 [51] Int. Cl. G01P 15/02 [58] Field of Search73/505, 515, 516 R, 510, 73/514, 517 A, 517 R [56] References CitedUNITED STATES PATENTS 2,365,218 12/1944 Rogers 73/71.4

2,498,118 2/1950 Weiss 73/505 3,085,443 4/1963 Manteuffel 73/5053,540,268 11/1970 Kantola et a1. 73/515 X 3,541,865 ll/197O Brown 73/5153,768,374 10/1973 Shin Ito et al. 73/515 X FOREIGN PATENTS ORAPPLICATIONS 1,054,646 10/1953 France 73/517 A Primary Examiner.lames.l. Gill Attorney, Agent, or FirmGausewitz, Carr & Rothenberg 57]ABSTRACT An antiskid braking system which includes valve means forcontrolling the application of operating pressure to the brakes, so asto rapidly release and then more gradually allow application of thebrakes when a skid is indicated, the valve means being operated by theoutput of a fluid amplifier means which, in turn, is operated by signalsfrom a linear accelerometer that moves in the path of the vehicle and anangular accelerometer that rotates with the wheel, each accelerometerincluding a seismic mass positioned by impinging fluid discharged froman adjacent outlet and relatively movable to vary the restriction of thefluid discharged to produce signals indicating acceleration anddeceleration.

1 Claim, 9 Drawing Figures AIB SUPPLY atent Dec. 16,1975 SheetlofS926,059

US. Patent Dec. 16, 1975 Sheet2of5 3,926,059

suPPLY 9.. mm. a.

Sheet 3 of 5 U.S. Patent Dec. 16, 1975 Sheet4of5 3,926,059

\37 I 7 ////k 7/ V///// FUJHNC NR SUPPLY ACCELEROMETER This is adivision of application Ser. No. 277,676, filed Aug. 3, 1972, now US.Pat. No. 3,804,471.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to an accelerometer and antiskid braking system.

2. Description of Prior Art There has been an increasing recognition ofthe importance of antiskid braking systems for vehicles, such as trucksand automobiles. Several of such systems have been designed, but theyhave not achieved widespread acceptance. The antiskid devices which havebeen made available for purchase operate through complex electronicfeedback circuits, and are sufficiently expensive to be prohibitive incost for all but a minor segment of the market. Also, some of theseunits detract from the maximum braking effect which otherwise would beobtainable for the vehicle. Maintenance problems and uncertainreliability also may be present with such prior units.

SUMMARY OF THE INVENTION The present invention overcomes the difficultyof prior devices, resulting in an antiskid system which is economical toconstruct and fully reliable in its operation, while effectivelyaccomplishing rapid vehicle deceleration. The system includes a linearaccelerometer which is attached to the vehicle so as to travel in thepath that the vehicle takes. There is, in addition, an angularaccelerometer for each of the wheels of the vehicle for which skidcontrol is to be provided.

The linear accelerometer includes a seismic mass, which may be a spherewhich is positioned between two opposed fluid streams, whichconveniently are airstreams. Under conditions of constant velocity, theseismic mass will be equidistant between the two fluid outlets. However,if acceleration is experienced, one of the outlets will be moved closerto the seismic mass and the other will be separated from it by anequivalent amount. The result is an increase in static pressure in thedischarge chamber upstream of the one fluid outlet and a correspondingdecrease in pressure in the fluid chamber upstream of the other outlet.The difference between these two pressures is proportional to the amountof acceleration experienced.

The angular accelerometer may include a pair of seismic masses, such asspheres, at the ends of a rigid arm pivotally mounted at a point midwaybetween the two masses. Each sphere is located adjacent a fluid outlet,the outlets being positioned to discharge with parallel streams whichimpinge upon the spheres. In the absence of angular acceleration, thefluid streams keep the spheres equidistant from the two fluid outlets,and the pressures in the discharge chambers are equal. Upon experiencingangular acceleration, however, one fluid outlet will be moved closer toits adjacent sphere and the other away from the adjacent sphere. Theresult is an increase in pressure in one discharge chamber and adecrease in pressure in the other. The differential is proportional tothe amount of angular acceleration.

Alternatively, the spheres may be unconnected and each located betweenopposed fluid streams. When angular acceleration occurs, each spherewill move closer to one fluid outlet and farther away from the other.The pressures in the chambers which experience 2 the pressure increaseare added in a fluid amplifier and those in the other two chambers thatexperience the pressure decrease also are added in the amplifier. Thetwo resulting pressures then are subtracted, giving a resulting pressurewhich is proportional to the applied angular acceleration.

The angular accelerometer also may include four spherical massesarranged in a generally square pat tern, in which event two fluidamplifiers are used in appropriately adding pressure signals andsubtracting others to obtain a resulting output proportional to angularacceleration.

In a vehicle braking system, such as one for pneumatic truck brakes, thesignal from the angular accelerometer is subtracted from that of thelinear accelerometer in a summing proportional fluid amplifier. Theresulting signal is applied to the inputs of a digital fluid amplifier.The output of the latter device is applied across either end of acontrol valve. This valve is in the line that conducts pressurized air,as directed by the brake pedal, to the actuating chamber for applyingthe brakes. In the event a skid commences, the signal from the angularaccelerometer will greatly exceed that from the linear accelerometer.This causes the digital ampli fier to become saturated, producing asignal which immediately shifts the control valve to a position where itblocks the pressure line from the brake pedal so that it no longer hasaccess to the brakes. At the same time, it vents the brake actuator toatmosphere so that the brakes are released. Then, as the wheelaccelerates, it produces an opposite signal from the digital amplifier,which moves the control valve in the opposite direction to permit thebrakes to be reapplied. The latter movement, through a check valve andrestrictor, is controlled so that brakes are applied more gradually thanthey are released. The cycle is repeated rapidly as long as the wheeltends to skid, as the brakes are continually applied and then released,which effectively slows down the vehicle while preventing a skid.

The same arrangement of accelerometers and ampli fier is used inconjunction with a hydraulic brake system. In this event, the signalfrom the amplifier will move an additional control valve which blocksthe application of hydraulic fluid to the wheel cylinder. At the sametime, the air control valve is moved to vent an accumulator toatmosphere, which, in turn, permits fluid to be bled from the wheelcylinder into a chamber of the accumulator. The air valve is moved morerapidly back to its original position by the signal from the thenaccelerating wheel than is the hydraulic control valve. Accordingly, theaccumulator becomes pressurized to return the hydraulic fluid t0 thewheel cylinder. The cycle repeats over and over so long as there is atendency for the wheel to skid.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a side elevational view,partially in section, of a linear accelerometer;

FIG. 2 is a side elevational view, partially in section, of an angularaccelerometer;

FIG. 3 is a side elevational view, partially in section of a differentembodiment of the angular accelerometer;

FIG. 4 is a side elevational view, partially in section, of a furtherembodiment of the angular accelerometer;

FIG. 5 is a plan view illustrating the components of an antiskid systemassociated with a vehicle having pneumatic brakes;

FIG. 6 is a schematic view of the part of the antiskid system of FIG.used for each wheel of the vehicle;

FIG. 7 is a schematic view of a portion of the arrangement of FIG. 6,showing certain components in alternate positions;

FIG. 8 is a schematic view of the antiskid system as used for each wheelin a hydraulic braking system; and

FIG. 9 is a schematic view of a portion of the arrangement of FIG. 8,with certain parts in their alternate positions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The braking system of thisinvention utilizes a combination of linear and angular accelerometersarranged such that the brakes of a vehicle will be released in the eventa skid is detected, and then reapplied on a rapidly repeating cycle. Theskid control prevents the locking of the wheels, continually limitingthe braking force so that it cannot cause the wheels to slide.

A linear accelerometer for use in this invention is shown in FIG. 1.This accelerometer, like all accelerometers, operates on the principleof Newtons Second Law of Motion, that is, acceleration of a body isdirectly proportional to the net force producing the acceleration andinversely proportional to the mass. In the accelerometer 10 of FIG. 1,the mass is a sphere ll of predetermined size and weight. The sphere 11is positioned between two opposed axially aligned openings l2 and 13 ofidentical size, which allow fluid to discharge from chambers 14 and 15.The sphere 11 is dimensioned so that it is permitted to move a limiteddistance between the two outlets. A cage 16 is provided around thesphere 11 between the outlets l2 and 13, which limits the movement ofthe sphere 11 to a linear path between the two outlets. The sphere 11cannot drop from its position between the outlets when the accelerometeris not in operation.

A pair of convergent fluid nozzles 18 and 19 communicates with thechambers 14 and 15, respectively. The nozzles 18 and 19 are suppliedwith fluid from passageways 20 and 21, which receive their fluid from aninlet 22.

The accelerometer 10, as well as the other accelerometers describedbelow, operates effectively on air, which normally can be made availableat a low cost, but any other fluid, such as hydraulic fluid, may be usedas well. In the examples given, air will be indicated as theaccelerometer fluid.

In operation of the accelerometer, air entering the inlet 22 is split toflow in equal volumes through the two passageways 20 and 21. From these,it discharges through the convergent nozzles 18 and 19 into the axiallyaligned cylindrical chambers 14 and 15. Air then flows outwardly throughthe discharge openings 12 and 13, impinging on opposite sides againstthe sphere 11. From there, the air escapes through the spaces 25 and 26between the edges of the openings 12 and 13 and the periphery of thesphere 11. The parts are proportioned such that each air escape area isless than the area at the adjacent outlet opening. In other words, thecross-sectional area of the space 25 is less than that of the outletopening 12, and the area of the space 26 is not as great as that of theoutlet 13. As a result, the two fluid streams are restricted at thelocations where they escapearound the sphere 11.

Under normal conditions, such as when the accelerometer 10 is moving ata constant velocity, there will be 4 equal flows of air through theoutlets 12 and 13, and the sphere 11 will be suspended by the opposingstreams midway between the two outlets. At this time, the pressure taps29 and 30 for the chambers 14 and 15 will indicate the same staticpressure for the two chambers.

In the event that the accelerometer 10 should experience acceleration inthe direction of the axis A of the chambers 14 and 15, and their outlets12 and 13, the sphere l 1 will move toward one of the outlets and awayfrom the other. The sphere 11 will tend to continue its movement at aconstant velocity, having no direct connection to the other componentsof the accelerometer which experience the acceleration. Therefore, thebody of the accelerometer will move relative to the spherical mass 11,bringing the outlet 12 or the outlet 13 closer to the sphere. In theevent the linear acceleration of the accelerometer 10 is in thedirection of the arrow, i.e., to the right as the device is shown inFIG. 1, the outlet 12 will move toward the sphere 11, while the outlet13 is shifted away from the sphere. The result is an increasedrestriction at the outlet 12 and less restriction at the outlet 13.Consequently, the pressure in the chamber 14 rises, while the pressurein the chamber 15 drops. The difference in these pressures, which can bedetected at the pressure taps 29 and 30, is directly proportional to theamount of acceleration of the accelerometer. Therefore, acceleration canbe computed upon reading the pressures in the taps 29 and 30 andsubtracting one from the other. Also, the pressure taps 29 and 30 canprovide a usable output signal proportional to acceleration, which canoperate other devices in a system.

Deceleration is indicated in the same manner that acceleration is shown.Assuming movement in the direction of the arrow in FIG. 1, decelerationof the accelerometer will bring the sphere 11 closer to the outlet 13and away from the outlet 12 as the sphere tends to continue at aconstant velocity. The pressure then rises in the chamber 15 and fallsin the chamber 14, with the difference being proportional to the rate ofdeceleration.

For indicating angular acceleration, the device may take the form shownin FIG. 2. Here the accelerometer 31 has two identical spheres 32 and 33of known mass and size mounted on arms 34 and 35, respectively, whichare of equal length and axially aligned. The rods are attached to ashaft 36 which is pivotally mounted on brackets 37 so as to be rotatableabout an axis perpendicular to the arms 34 and 35. The sphere 32 ispositioned adjacent the outlet 39 of a fluid chamber 40, while similarlythe sphere 33 is located next to the outlet 41 of a fluid chamber 42.The outlets 39 and 41 fall in the same plane, and the chambers 40 and 42are parallel so as to discharge airstreams that are perpendicular toextensions of the axes of the arms 34 and 35.

Pressurized air for the chambers 40 and 42 is supplied through an inlettee 44, where it is divided equally and discharged through convergentnozzles 45 and 46 into the chambers 40 and 42. This provides equalairflows through the outlets 39 and 41 so that equal forces are appliedto the spheres 32 and 33. Consequently, the spheres 32 and 33 are heldequidistant from their respective fluid outlets 39 and 41. Equalpressures then are realized in the chambers 40 and 42 and can bemeasured at the pressure taps 47 and 48.

In the event of an angular acceleration of the accelerometer 31 about anaxis coincident with, or parallel to,

the shaft 36 that mounts the arms 34 and 35, one fluid outlet will bemoved toward its adjacent sphere, and the other will move away from itsadjacent sphere, as relative rotation occurs about the shaft 36. Forangular acceleration in the clockwise direction, as the device is shownin FIG. 2, the relative movement will bring the fluid outlet 39 closerto the sphere 32. A corresponding movement of the fluid outlet 41 awayfrom the sphere 33' also occurs. The increased restriction at the outlet39 causes the pressure in the chamber 40 to increase. Similarly, thedecreased restriction at the outlet 41 allows the fluid to dischargemore freely from that opening, so that the pressure is reduced in thechamber 42. A differential pressure signal then is indicated by the twopressure taps 47 and 48. This pressure difference is directlyproportional to the angular acceleration of the unit.

Deceleration produces the opposite relative movement between thespherical mass and its adjacent fluid outlet, again generating apressure differential in the chambers 40 and 42. The difference inpressure is directly proportional to the rate of deceleration.

Linear acceleration does not affect the accelerometer 31 as the forcesthen imposed cancel out so as to produce no relative movement betweenthe spheres 32 and 33 and the body of the accelerometer. The linearaccelerating forces may be resolved into components in the direction ofthe axes of the arms 34 and 35, and normal thereto. The former forcecomponents cannot influence the positions of the spheres 32 and 33because of their connections to the arms 34 and 35. The force componentsnormal to the axes of these arms are the same for each sphere and socannot cause the arms to rotate.

Another form of angular accelerometer 50 is shown in FIG. 3. Thisaccelerometer, which may be considered as falling in a single plane,includes a spherical mass 51 positioned between axially aligned opposedfluid outlets 53 and 54, which discharge from chambers 55 and 56. Amatching sphere 57 is between a second pair of aligned fluid outlets 58and 59, which discharge fluid from chambers 60 and 61, respectively. Theaxes of the two sets of fluid outlets are parallel, and the spheres 51and 57 are at opposite locations. Fluid for the chambers 55 and 60 issupplied from an inlet tee 62, and discharged through converging nozzles63 and 64 in opposite directions and equal volumes into the chambers 55and 60. A corresponding inlet 65 receives fluid at the same pressure,discharging it equally through converging nozzles 66 and 67 to enter thechambers 56 and 61. Consequently, under constant velocity conditions,the masses 51 and 57 are suspended by opposing fluid streams midwaybetween their adjacent fluid outlets.

A line 69 extends from the chamber 55 to one side (the right, asillustrated) of a two-input summing fluid amplifier 70. This applies thestatic pressure of the chamber 55 to one input of the fluid amplifier70. A

pressure line 71 for the chamber 56 also is connected to the amplifier70, providing an input opposite from the pressure line 69. The pressuresin the chambers 60 and 61 also provide opposing inputs to the amplifier70. The chamber 60 is connected through a line 72 to the amplifier 70 onthe same side as that of the line 71. This is in opposition to thepressure input from the line 73 that extends to the amplifier from thechamber 61.

With this arrangement, the pressures in the chambers 56 and 60 areadded, the pressures in the chambers 55 and 61 are added, and the tworesulting pressures are subtracted. This produces a differentialpressure at the output taps 75 and 76 of the amplifier which isproportional to the difference of the two input differential pressures.

If an angular acceleration is experienced about an axis perpendicular tothe plane of the accelerometer 50, one of each set of fluid outlets willbe moved toward its adjacent spherical mass, and the other fluid outletwill move away from the spherical mass. As before, the pressure in oneof each pair of opposed chambers will rise because of an increasedrestriction at its outlet, while in the other chamber the pressure willbe reduced because of less restriction at the outlet. For accelerationin the clockwise direction, as the ac celerometer is shown in FIG. 3,the outlet 54 will be moved toward the sphere 51 and the outlet 53 willbe moved away from it, raising the pressure in the chamber 56 andreducing it in the chamber 55. At the same time, the outlet 58 willshift toward the sphere 57 and the outlet 59 away from this sphere,increasing the pressure in the chamber 60, while it decreases in thechamber 61.

The signals from the two chambers 56 and 60, where the pressure isincreased, are added by virtue of being connected to the same side ofthe amplifier 70. Similarly, the pressures of the two chambers 55 and61, which decreased from the acceleration, are added by being connectedto the opposite side of the amplifier 70. The resulting opposedpressures are subtracted in the amplifier 70, so that the differentialpressure across the output pressure taps 7S and 76 is proportional tothe applied angular acceleration.

Linear accelerations experienced by the accelerometer 50 cancel out anddo not influence the output signal. For example, if there is linearacceleration vertically as the accelerometer is shown in FIG. 3, theoutlet 54 will be urged toward the sphere 51 and a similar tendency willbe felt toward moving the outlet 59 toward the sphere 57. The result isto increase the pressure differential between the chambers 55 and'56,and to decrease the pressure differential between the chambers 60 and61. These pressure changes are experienced on opposite sides of thefluid amplifier 70, hence being subtracted from each other and producinga zero difference in the amplifier output.

The angular accelerometer 77, illustrated in FIG. 4, includes fourspherical masses 78, 79, 80 and 81. The accelerometer is in a squarepattern, essentially in a single plane, with these spherical massesbeing at the midpoints of the four sides. The mass 78 is intermediatethe outlets of chambers 82 and 83, which receive air from convergentnozzles 84 and 85, respectively. The sphere 79, located between chambers86 and 87, is reacted upon by fluid discharged from nozzles 88 and 89.Chambers 90 and 91 are supplied with air from convergent nozzles 92 and93, discharging it on opposite sides of the sphere 80. The final twochambers 94 and 95 similarly receive air from nozzles 96 and 97,respectively, which provides the opposing forces on the sphere 81. Theair supply 98 connects through a line 99 to the four diagonal inlets100, 101, 102 and 103 at the corners of the accelerometer. The air issplit into two branches at each inlet, resulting in equal flows throughall of the nozzles.

When the accelerometer 77 is subjected to angular acceleration about anaxis perpendicular to the plane of the accelerometer, four of the outletopenings will become more restricted, while the other four will beopened up to result in pressure differences in adjacent air chambers.For clockwise acceleration, there will be relative movement of thechamber 83 toward the sphere 78, the chamber 86 toward the sphere 79,the chamber 91 toward the sphere 80, and the chamber 94 toward thesphere 81. As a result, pressure will increase in the chambers 83, 86,91 and 94. A corresponding reduction in pressure will be experienced inthe chambers 82, 87, 90 and 95.

Two two-input summing amplifiers 105 and 106 receive the pressuresignals from the chambers of the accelerometer 77. In the arrangementshown, the signals from the chambers 87 and 90, on opposite sides of theaccelerometer, are added, being connected through lines 107 and 108 tothe left side of the amplifier 105. These two pressures are reduced bythe clockwise acceleration of this example. On the opposite side of theamplifier 105, the signal from the chamber 86 is received through line109 and that of the chamber 91 through line 110. These chambers, whichexperienced pressure increases from the acceleration, are opposed to thechambers 87 and 90.

In a similar manner, the other pressure chambers on the two remainingopposite sides of the accelerometer 77 are connected to the amplifier106. Chamber 82, which had a decrease in pressure from acceleration,connects through line 112 to the left side of the amplifier 106, whilechamber 95, which likewise lost pressure, through line 113 connects tothe same side of the amplifier 106. On the opposite side of theamplifier 106, the chamber 83 is connected through a line 114, and thechamber 94 is connected through a line 115. The latter two chambersincreased in pressure from the acceleration.

The output signals of the two amplifiers 105 and 106 are connected to athird two-input summing amplifier 117. Lines 1 l8 and 119 connect oneside of the amplifiers 105 and 106 respectively, to the same side of theamplifier 117. Lines 120 and 121 connect the opposite sides of theamplifiers 105 and 106 to the opposite side of the amplifier 117. Thedifferential pressure then present across the outputs 122 and 123 of theamplifier 117 is directly proportional to the acceleration experiencedby the accelerometer.

Linear acceleration signals cancel out of the accelerometer 77 in amanner similar to that of the accelerometer 50.

All three accelerometers will operate satisfactorily in a vehicleantiskid system. The accelerometer 50 is subject to inaccuracy if notconfined to rotation in the same plane as that of the accelerometer.However, this normally is no problem in a vehicle system. Because of itssimplicity, the accelerometer 31 of FIG. 2 is preferable, while thegreater complexity and expense of the accelerometer 77 of FIG. 4 make itthe least desirable.

An antiskid system for controlling the application of braking forces ina pneumatic braking system is shown schematically in FIG. 5. The truck124 illustrated has wheels 125 with brakes 126 of conventional design.Pressurized air for operation of the brakes 126 is conducted throughlines 127 from a source 128. The operation of the brake pedal, through aconventional arrangement, determines the amount of pressure existing inthe lines 127 for application of the brakes.

Instead of connecting directly to the brake actuators, as ischaracteristic ordinarily of truck braking systems, the lines 127connect to control units 129, one of which 8 is carried by the truck 124adjacent each wheel, or set of wheels, which is to be prevented fromskidding. In the event of an incipient skid at any wheel, the adjacentcontrol unit governs the actual braking force to be applied to thewheel, irrespective of the pressure existing in the pneumatic supplyline 127.

Also provided for each wheel is a linear accelerometer, such as theaccelerometer 10 of FIG. 1, suitably mounted on the axle or frame 130 sothat its longitudinal axis is in the direction of the path of movementof the truck 124. An angular accelerometer, appropriately the angularaccelerometer 31 of FIG. 2, is included for each wheel, arranged torotate with the wheel 125. The linear and angular accelerometers providesignals which determine the operation of the control unit 129 and hencethe application of the braking force in the event of a skid condition.

The various components for each wheel of the antiskid system are shownin FIG. 6. The actuator 131 for applying the brakes at the wheel isconventional, including a rod 132 movable by a diaphragm 133 whenpressurized air is received in the chamber 134 in back of the diaphragm.This movement is to the right, as the device is illustrated, and appliesthe brakes. When pressure in the chamber 134 is relieved, a springreturn moves the rod 132 to the left and the brakes are released.

The brake pressure line 127 connects to the inlet 135 of a control valve136 which is included in the brake control unit 129. The outlet 137 ofthe valve 136 connects through a line 138 to the chamber 134 of theactuator 131. Within the valve 136 is a spool 139 having a center lobe140 and additional lobes 141 and 142 at its ends. Under normalconditions, when the wheel 125 has no tendency to skid, the spool 139 iscentered by compression springs 143 and 144 which engage the end lobes141 and 142. In this position, shown in FIG. 6, pressurized fluid fromthe line 127 is permitted to flow through the valve 136 to pressurizethe chamber 134 via the line 138. This allows for operation of thebrakes in the conventional manner.

However, if the valve spool should be moved to the left, as illustratedin FIG. 7, the center lobe 140 then will close 011 the valve inlet 135so that pressure from the line 127 no longer can be transmitted throughthe valve 136 to the actuator 131. In this position of the valve, thelobe 140 uncovers a port 145 that then provides access to the valvechamber between the lobes 140 and 142. The line 138 to the actuatorchamber 134 branches and connects to the valve port 145. An additionalport 146 connects the space in the valve chamber between the lobes 140and 142 to the atmosphere. With the valve spool 139 moved to theposition of FIG. 7, pressure from the chamber 134 can vent to theatmosphere. This pressure bleeds through the line 138 and the valve port145 to the valve chamber, where it exhausts through the port 146.Therefore, this position of the spool 139 causes release of the brakesof the vehicle by relieving the pressure within the brake actuator 131.

The linear accelerometer 10 receives its supply of operating fluid froma fluidic air supply 147 to which it connects by a line 148. Anadditional line 149 from the air supply 147 extends to the angularaccelerometer 31. Assuming vehicle movement to the left, and counterclockwise rotation of the angular accelerometer 31, the output pressurelines 150 and 151 from the left and right-hand sides, respectively, ofthe angular accelerometer 31 are connected to the opposite sides of asumming proportional amplifier 152. Conversely, lines 153 and 154connect from the leftand right-hand sides of the linear accelerometer tothe leftand right-hand sides, respectively, of the amplifier 152. Inthis way, the signal from the angular accelerometer 31 is subtractedfrom the signal of the linear accelerometer 10. A connection 155supplies pressurized air from the source 128 as the operating fluid ofthe amplifier 152.

The outputs from the amplifier 152 are connected through lines 157 and158 to the two sides of a digital fluid amplifier 159. This connects theleft output of the amplifier 152 to the left-hand side of the amplifier159, and the right output of the amplifier 152 to the righthand side ofthe amplifier 159, as the components are illustrated. The digitalamplifier 159 is supplied with operating fluid from a line 160 connectedto the source of pressurized air 128. The left-hand output of thedigital amplifier 159 is connected through a line 161 to a port 162 atthe left-hand end of the control valve 136. The other output, from theright side of the amplifier 159, connects through a line 163 to theright-hand end port 164 of the control valve 136. A check valve 165 inthe line 163 permits flow only away from the amplifier 159 and towardthe port 164. The check valve 165 is bypassed by a line 166 in whichthere is a restricting orifice 167.

If the wheel 125 to which the angular accelerometer is connected shouldcommence a skid, it will experience a rapid angular deceleration. Underthese circumstances, the linear deceleration will be much less becausethe skidding wheel has a reduced sliding coefficient of friction withrespect to the pavement, and will not effectively slow down the vehicle.The result is a wide disparity between the pressure signals of theangular and linear accelerometers. A sufficient difference between thesignals from the angular accelerometer and the linear accelerometerproduces a relatively high pressure in the output line 157 compared withthat in the other output 158 of this amplifier. When this signal isapplied to the control ports of the digital amplifier 159, it causes thelatter amplifier to become saturated. The result is an increasedpressure in the line 163, which, in turn, applies pressure through theinlet port 164 to the right-hand end of the spool 139. This drives thevalve spool 139 to the left as the device is shown, shifting it from theposition of FIG. 6 to that of FIG. 7. When that occurs, the pressurefrom the brake pressure line 127 is blocked by the center lobe 140 ofthe spool 139 and cannot reach the brake actuator 131. Simultaneously,the chamber 134 of the actuator 131 vents through the line 138 and theports 145 and 146 to the atmosphere. This releases the brakes.Therefore, as soon as the wheel 125 tends to slide, its deceleration issensed and used to release the brakes at that wheel.

When the wheel stops its skid, the signal from the angular accelerometerbecomes reversed. This is because the wheel then accelerates rapidlyfrom its rotationally locked condition to its normal angular velocity.The angular accelerometers signal again greatly exceeds that of thelinear accelerometer, but because it is reversed it will create arelatively high pressure in the line 158. This saturates the digitalamplifier 159 on the opposite side, so that the pressure in the line 161greatly exceeds that in the line 163. This biases the valve spool 139 tothe right, back toward its original position. However, the check valve165 will not permit reverse flow in the line 163 that connects to therighthand end port 164. Instead, the fluid in the line 163 can onlybleed relatively slowly through the restricted orifice 167 in the bypass166. Consequently, while the brakes are released almost instantaneouslyupon the advent of a skid, the control valve spool 139 .can be returnedto its central neutral position only at a much slower rate as the fluidbleeds in the reverse direction through the line 163. Therefore, aperiod of time elapses before reapplication of braking pressure from theline 127 through the valve 136 to the brake actuator 131. Thus, there isan extremely rapid release of the brakes, but a more gradualreapplication of them.

If, when the brakes are reapplied, the wheel again should tend to lock,the cycle will be repeated as the saturated signal from the amplifier159 will cause the release of the brakes as a consequence of the rapiddeceleration of the wheel. The cycle is repeated over and over veryrapidly, with sliding of the wheel always being precluded. A brakingeffect is realized each time the valve 136 is moved back to its neutralposition so that the vehicle is slowed down as the skid controloperates. The system may be constructed so as to cause complete or onlypartial release of the brakes as the control valve 136 is operated.

The system of FIG. 8 provides an antiskid arrangement for hydraulicbrakes. The same source of control signals may be used as in the systemfor pneumatic brakes shown in FIG. 6. Thus, the linear accelerometer 10,the angular accelerometer 31, summing proportional amplifier 152 anddigital amplifier 159 again are included and connected together asbefore.

The output of the digital amplifier 159 connects by lines 168 and 169 tothe opposite ends of a hydraulic control valve 170. There is, inaddition, an air control valve 136, which is in parallel with the valve170, connected to the output of the amplifier 159 by lines 171 and 172.The valve includes a spool 173 normally centered by compression springs174 and 175 at its ends so that it assumes the position of FIG. 8. Theends of the lobes 176 and 177 of the spool 173 are engaged by thesprings 174 and 175, and also may be reacted upon by air in the lines168 and 169. However, the central part of the valve 170, between thelobes 176 and 177, is sealed from the ends and serves to controlhydraulic fluid at inlet and outlet ports 178 and 179, respectively. Aline 181 connects to the inlet port 178 and also to the master cylinder(not shown) of the vehicles braking system. Hydraulic line 182 connectsthe outlet port 179 of the valve 170 with the wheel cylinder 183 of thevehicles brakes. Opposed pistons 184 and 185 in the wheel cylinder 183engage brake shoes 186 and 187. With the hydraulic control valve 170 inthe neutral position shown in FIG. 8, the brakes operate in the normalmanner, with pressurized hydraulic fluid from the line 181 passingthrough the valve 170 to the interior of the wheel cylinder 183 to forcethe pistons 184 and 185 outwardly. This, in turn, causes the brake shoes186 and 187 to be applied to the brake drum for decelerating thevehicle.

High-pressure air from a source 188 connects through a line 189 to theinlet port 135 of the air control valve 136. When the spool 139 is inits central position, this air is conducted through the valve 136 into aline 190, which connects to a chamber 191 of an accumulator 192. Withinthe chamber 191, the highpressure air reacts against a diaphragm 193, onthe opposite side of which is a piston 194. The pressure of the air inthe chamber 191 against the diaphragm 193 1 1 biases the piston 194against the end wall 195 of the accumulator 192, or some other stop tolimit the outward travel of the piston.

Hydraulic line 197 connects to the accumulator 192 at the wall 195 andalso is connected to the hydraulic line 182 downstream of the valve 170.Consequently, the outer face of the accumulator piston 194 is subjectedto hydraulic pressure equal to that in the line 181 from the mastercylinder. However, the area of the piston 194 and the maximum pressurein the hydraulic system are correlated with the size of the diaphragm193 and the air pressure in the chamber 191, so that the piston 194normally is held in engagement with the end wall 195. Therefore, thepiston 194 does not move under ordinary conditions and does not affectthe application of pressurized hydraulic fluid to the brake cylinder183.

The hydraulic control valve 170 is bypassed by a line 198 whichinterconnects this valves inlet and outlet lines 181 and 182,respectively. A check valve 199 is in the line 198, permitting flow onlyfrom the line 182 toward the line 181. In normal braking, of course, thepressures are substantially equal in the lines 181 and 182 so that thereis no flow through the bypass 198.

In the event of a skid, the amplifier 159 will become saturated in themanner described above in connection with the system of FIG. 6. Thisproduces an increase in pressure in the line 169 compared with that inthe line 168. Consequently, the spool 173 of the valve 170 is driven tothe left, as the device is shown, causing the lobe 177 to close theinlet port 178. This blocks off the source of pressurized hydraulicfluid from access to the wheel cylinder 183.

Simultaneously, the amplifier 159 provides greater air pressure in theline 172 than in the line 171 and forces the spool 139 of the valve 136to the left. This causes the center lobe 140 to close off the inlet port135, shutting off the high-pressure air supply line 189. The centrallobe 140 then also uncovers the port 145 which is connected to the line190 that leads to the accumulator 192. This allows air to bleed from thechamber 191 through the line 190 and the port 145 into the interior ofthe valve 136 between the lobes 140 and 142. This air exhausts to theatmosphere through the vent port 146. Therefore, the air pressureagainst the diaphragm 193 is relieved. With the piston 194 of theaccumulator 192 no longer being biased outwardly, it is moved inwardlyby the hydraulic pressure as fluid from the wheel cylinder 183 can bleedthrough the line 182 and the line 197 to the accumulator. This releasesthe brakes. A stop 201 limits the travel of the piston 194 inwardly tothe position shown in FIG. 9, where it accepts a predetermined quantityof hydraulic fluid sufficient to relieve the pressure in the wheelcylinder 183 so that the wheel no longer skids.

With the brakes released, the wheel accelerates back to substantiallyits original velocity. This causes the pressure signal of the angularaccelerometer 31 to reverse, resulting also in a reversal in therelative pressures in the lines 168 and 169 and the lines 171 and 172.Thus, the control pressure from the amplifier 159 urges the spool 139 ofthe valve 136 back toward its central position. Similarly, the signalfrom the amplifier 159 biases the spool 173 of the valve 170 to theright toward its original centered position.

The return movement, of both valve spools is regulated by restrictionsagainst fluid flow in the reverse direction. In the line 169, thisincludes a check valve 12 202 allowing flow only toward the valve 170,together with a bypass 203 with a restricted orifice 204. Another checkvalve 205 is included in the line 172 so that full flow can go onlytoward the valve 136. Return flow must go via the bypass 206 in which isa restricted orifice 207. The restricted orifices 204 and 207 areproportioned such that the spool 139 of the valve 136 is allowed toreturn to its neutral position much more rapidly than is the spool 173of the hydraulic control valve 170. Consequently, after the brakes havebeen released, the valve spool 139 is moved back to its center positionat a time when the valve spool 173 still continues to block pressurizedfluid from the line 181.

With the valve spool 139 centered, high-pressure air again is conductedthrough the line 189, the valve 136 and the line to the chamber 191. Asdescribed above, the outward force exerted by the diaphragm 193 when theaccumulator 192 is pressurized exceeds the inward force exerted by thehydraulic fluid on the piston 194. The air pressure in the accumulator192 then causes the piston 194 to be returned to its outer position inengagement with the end wall 195. This, in turn, conducts the hydraulicfluid through the lines 197 and 182 to the wheel cylinder 183. Thus, theaccumulator 192 reapplies the brakes.

The accumulator 192 will not apply the brakes at a pressure greater thanthat existing in the line 181. This is because a higher pressure in thelines 182 and 197 will bleed through the line 198 and the check valve199 to equalize with the pressure in the line 181. Therefore, the brakesare reapplied only up to the maximum pressure being commanded by thedriver at the time of the reapplication of the brakes.

If when the brakes are reapplied a skid again is detected, the cyclewill repeat. That is to say, the saturated signal will cause the valve136 to dump the air pressure from the accumulator 192, allowing thehydraulic fluid again to bleed from the wheel cylinder 183. The cyclecontinues, stopping the skid at the outset and slowing the vehicle untilsuch time as the pressure from the master cylinder no longer will tendto lock the wheel. The system cycles very rapidly so that there isalways complete control of the action of the wheel.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit and scope of thisinvention being limited solely by the appended claims.

I claim:

1. An accelerometer comprising first, second, third and fourth seismicmasses,

said masses being of equal size, shape and mass,

a pair of chambers positioned one on either side of each of said masses,each of said chambers including an outlet opening facing the adjacentseismic masses, said outlet openings being opposed and axially alignedfor each of said seismic masses, a source of pressurized fluid forproviding fluid streams discharging through said outlet openings,whereby each of said masses is suspended between opposed fluid streamsand is movable toward and away from the adjacent outlet openings,

said fluid streams for said first and second seismic masses beingsubstantially parallel,

said fluid streams for said third and fourth seismic masses beingsubstantially parallel and normal to the "direction of said fluidstreams for said first 13 and second seismic masses, said masses andchambers being in substantially a square pattern, means for detectingthe static pressure in each of said chambers for obtaining signals ofpressure increase from relative movement of a seismic mass toward anoutlet opening and of pressure decrease from

1. An accelerometer comprising first, second, third and fourth seismicmasses, said masses being of equal size, shape and mass, a pair ofchambers positioned one on either side of each of said masses, each ofsaid chambers including an outlet opening facing the adjacent seismicmasses, said outlet openings being opposed and axially aligned for eachof said seismic masses, a source of pressurized fluid for providingfluid streams discharging through said outlet openings, whereby each ofsaid masses is suspended between opposed fluid streams and is movabletoward and away from the adjacent outlet openings, said fluid streamsfor said first and second seismic masses being substantially parallel,said fluid streams for said third and fourth seismic masses beingsubstantially parallel and normal to the direction of said fluid streamsfor said first and second seismic masses, said masses and chambers beingin substantially a square pattern, means for detecting the staticpressure in each of said chambers for obtaining signals of pressureincrease from relative movement of a seismic mass toward an outletopening and of pressure decrease from relative movement of a seismicmass away from an outlet opening as a result of angular deceleration ofsaid chambers, and means for adding said signals so as to obtain acomposite output signaL proportional to angular acceleration.